COLOGNO MONZESE, Italy, Sept 4 (Reuters) - Shareholders in Italian broadcaster Mediaset on Wednesday backed a plan to create a pan-European media group under a new Dutch holding, fending off opposition from its second biggest shareholder Vivendi.

The vote is the latest blow for the French conglomerate led by media tycoon Vincent Bollore, which opposes the plan saying the new governance structure strengthens the hold of Mediaset's biggest shareholder, the family of former Italian Prime Minister Silvio Berlusconi.

Under the plan, both Mediaset and its Spanish unit would be merged into a Dutch company dubbed MediaForEurope (MFE).

Mediaset would use this as a platform for continental alliances with other broadcasters and tackle competition from video-streaming services like Netflix and Amazon Prime Video.

Mediaset bought a 9.6% stake in ProSiebenSat.1 Media in May and is counting on the German broadcaster and other prospective partners to join forces through MFE to use a common technology platform to provide streaming services across Europe.

Vivendi, which has plans of its own to become a European media powerhouse, has been a hostile Mediaset shareholder since Bollore and Berlusconi fell out in 2016 over an aborted pay-TV deal.

After the failed pay-TV sale, the French group built a 29% stake in Mediaset - a holding that the Italian group considers illegitimate. The two sides have been in a legal war ever since.

A Milan court granted Vivendi the right to vote on Wednesday only with the 9.99% Mediaset stake it directly owns - not enough to block the deal on its own.

Two-thirds of Vivendi's stake in Mediaset are held through an arms-length trust which in the past has been barred via court rulings from voting at shareholder meetings, and which Mediaset prevented from participating in Wednesday's meeting.

Vivendi slammed Mediaset's decision to prevent the trust from voting and vowed to challenge the corporate overhaul in court.

"Mediaset is disregarding the most basic shareholder rights and principles of corporate governance with the sole objective of favouring [the Berlusconi family's holding company] Fininvest, without even recognising a premium to minorities," Vivendi said.

WITHDRAWAL?

The French media group could still throw a spanner in the works if it decides to sell its Mediaset stake - as the corporate overhaul is conditional on no more than 180 million euros being spent to mop up the shares of investors who head for the door - well below the value of Vivendi's stake.

Vivendi has not made clear whether it is prepared to sell its holding. Doing so would translate into a loss of around 320 million euros for the French group.

Speaking to reporters after the meeting, Mediaset CEO Pier Silvio Berlusconi said he was convinced Vivendi would not exercise its withdrawal rights.

Mediaset shares closed up 1.3% at 2.8170 euros, slightly above the price of 2.77 euros a share at which Vivendi could sell its stake if it decided to head for the door.

Some sources have said Bollore might prefer to stay on as an investor in the hope that court rulings in his favour could eventually allow him to increase his sway over Mediaset.

Vivendi has also bought a stake of around 1% in Mediaset's Spanish unit. A source close to the matter said this was so it could attend a separate shareholder meeting on the corporate overhaul in Madrid on Wednesday and take its fight to a Spanish court if needed. (Additional reporting by Mathieu Rosemain and Gwenaelle Barzic in Paris Editing by Keith Weir and Jane Merriman)